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Ectopic Pregnancy Surveillance, United States, 1970-1985

Herschel W. Lawson, M.D. Hani K. Atrash, M.D., M.P.H. Audrey F. Saftlas, Ph.D., M.P.H. Adele L. Franks, M.D. Evelyn L. Finch Joyce M. Hughes Division of Reproductive Health Center for Chronic Disease Prevention and Health Promotion

Ectopic pregnancy is now one of the leading causes of maternal death in the United States. In 1984 and 1985, both the numbers and rates of ectopic pregnancy increased. Since the rate of ectopic pregnancy remained unchanged for white women, the rate increase appears to be driven by the increasing rate among women of black and other races. Although ectopic pregnancies accounted for only 1.5% of the total pregnancies in 1984 and 1985, they accounted for 14% of the total maternal deaths in 1984 and for 11% of those deaths in 1985. However, the case-fatality rate for 1985 decreased to 4.2/10,000 ectopic pregnancies, down from the 35.5 deaths/10,000 ectopic pregnancies reported in 1970. Several factors may contribute to the increase in ectopic pregnancies, including heightened awareness of the condition, improved diagnostic technology, and possibly the higher prevalence of risk factors (e.g., acute and chronic salpingitis and sexually transmitted diseases) and the lower prevalence of protective factors (e.g., decreased use of oral contraceptives). Heightened awareness of the condition and improved technology may also be factors resulting in the decreased case-fatality rate. INTRODUCTION

Ectopic pregnancy is one of the leading causes of maternal deaths in the United States, and it continues to be an important health problem (1). This complication of pregnancy results when the fertilized ovum implants anywhere other than the endometrial lining of the uterus (2). Ectopic pregnancies represented 1.5% of the total pregnancies in both 1984 and 1985 (1). The condition takes its toll in fetal loss, in the number of work days lost during hospitalization and recuperation of young women who are primarily healthy, and in the financial burden of caring for these women.

CDC has previously reported data on ectopic pregnancy for 1970-1983 (3-5). This surveillance report includes data for 1984 and 1985. METHODS

The numbers of ectopic pregnancies presented in this report are estimated from data collected by the National Center for Health Statistics (NCHS) as part of the ongoing National Hospital Discharge Survey (NHDS). The NHDS, which is conducted each year, uses a sample of approximately 400 nonfederal, short-stay hospitals that represent all 50 states and the District of Columbia. Demographic data, final diagnoses, and surgical procedures shown on the medical record face sheets are abstracted from a sample of medical records from each designated hospital. The more than 200,000 medical records included in the sample every year are weighted to represent approximately 30 million hospital admissions.

The diagnosis of ectopic pregnancy is based on those hospital discharge records with the diagnosis code 631 according to the International Classification of Diseases, Eighth Revision, Adapted for Use in the United States (ICDA-8) for 1970-1978 (6), and on those abstracts with the diagnosis code 633 according to the Ninth Revision (ICD-9) for 1979-1985 (7). The number of deaths caused by ectopic pregnancy is based on U.S. vital statistics collected by NCHS. Rates for ectopic pregnancy were calculated by dividing the estimated number of ectopic pregnancies by the total number of reported pregnancies. "Total pregnancies" is defined as the sum of live births, legally induced abortions, and ectopic pregnancies. Data for live births were obtained from NCHS natality statistics (8), and data for induced abortions were obtained from CDC's abortion surveillance system. Death-to-case rates were calculated by dividing the number of deaths caused by ectopic pregnancy by the estimated number of ectopic pregnancies. These rates were then reported as deaths per 10,000 cases (5). Total "person-days hospitalized" was calculated by multiplying the total estimated number of ectopic pregnancies by the average length of stay for each year.

The U.S. Department of Commerce, Bureau of Census, has defined the four geographic regions of the United States used in this report (Northeast, Midwest, South, West). For the calculation of ectopic pregnancy rates, women were grouped into three age categories: 15-24, 25-34, and 35-44 years of age. For the analysis of mortality from ectopic pregnancy, women were grouped into six age categories: 15-19, 20-24, 25-29, 30-34, 35-39, and 40-44 years. Race-specific rates for the categories "white" and "black and other" were used. If race was not included in the medical records, ectopic pregnancies were redistributed according to the racial distribution of cases for which race was recorded. Estimates of the number of ectopic pregnancies have been rounded to the nearest hundred. The rounding and redistribution of cases with unknown race sometimes cause the sum of numbers to be different from the total. Rates were calculated from the unrounded estimates. RESULTS

In 1984 and 1985, the numbers and rates of ectopic pregnancies increased, continuing the previously reported trend (Table 1, Figure 1). Sixty-one percent of the ectopic pregnancies in 1984 and 1985 occurred among 25- to 34-year-old women. In 1984 and 1985, the rates of ectopic pregnancies for white women remained unchanged (13.6/1,000 reported pregnancies in 1983, 13.5 in 1984, and 13.3 in 1985). However, the rates for women of black and other races increased from 15.5/1,000 in 1983 to 19.3 in 1984 and to 21.3 in 1985. In 1983, women of black and other races had a risk of ectopic pregnancy 1.1 times higher than that of white women. The risk among women of black and other races rose to 1.4 times that among white women in 1984 and to 1.6 times that among white women in 1985.

For the period 1970-1985, approximately 716,800 ectopic pregnancies occurred among women ages 15-44 in the United States; the overall rate was 10.0/1,000 reported pregnancies. From 1970 through 1985, the total number of ectopic pregnancies increased more than fourfold, from an estimated 17,800 in 1970 to 78,400 in 1985. The rate for all women combined increased more than threefold, from 4.5 in 1970 to 15.2 in 1985. When stratified by race, the rates increased more than threefold both for white women (from 4.0 in 1970 to 13.3 in 1985) and for women of black and other races (from 7.1 in 1970 to 21.3 in 1985). When numbers of ectopic pregnancies were combined into 4-year periods (1970-1973, 1974-1977, 1978-1981, and 1982-1985) and stratified by race, the rates for each racial group had increased from the earliest years (1970-1973) to the latest years (1982-1985) by the following factors: between twofold and threefold for all races combined, almost threefold for white women, and almost twofold for women of black and other races (Table 2). As reported earlier (5), the risk of ectopic pregnancy increased with age and was highest for women 35-44 years old (Table 3, Figure 2). White women 35-44 years of age had a threefold higher risk of ectopic pregnancy than white women 15-24 years of age, whereas women of black and other races 35-44 years of age had a fourfold higher risk than women of black and other races ages 15-24.

Overall, during the period 1970-1985, the rates of ectopic pregnancies for the four geographic regions were similar; the highest rates occurred in the Midwest and West (Table 4). However, race- and region-specific rates varied. For white women, the rate was highest in the West; for women of black and other races, the rate was highest in the Midwest.

In 1983, the average reported length of hospital stay for women who had ectopic pregnancies was 4.8 days. In both 1984 and 1985, the average length of stay was 4.5 days, a decrease from previous years. In 1984, ectopic pregnancy accounted for 339,300 total person-days of hospitalization, and in 1985 that figure increased to 352,800. Both figures represent increases over previous years and reflect the continued rise in the reported numbers of ectopic pregnancies. The average length of stay for the period 1970-1985 was 5.6 days, and the total person-days of hospitalization during that period was 4,019,100.

In 1984, 39 maternal deaths (14% of all such deaths) were related to ectopic pregnancy (Table 5). In 1985, this figure dropped to 33 (11%). The death-to-case rate decreased to 5.2 in 1984 and to 4.2 in 1985, down from the 5.3 reported in 1983 (Figure 3). In 1984 and 1985, women of black and other races had a death-to-case rate that was four times higher than that for white women.

Between 1970 and 1985, a total of 716 women died as a result of an ectopic pregnancy. Overall, the death-to-case rate has decreased between eightfold and ninefold since the first reporting period in 1970. Women of black and other races continue to have a higher rate of death related to ectopic pregnancy. For the 16-year reporting period, the case-fatality rate for women of black and other races was 3.5 times higher than that for white women (Table 6). Teenagers of black and other races had the highest rate of death related to ectopic pregnancy. The rate for this group was 5.5 times higher than that reported for white teenagers (Figure 4). DISCUSSION

Overall, the number and rate of ectopic pregnancies have increased every year from 1970 through 1985. Chow et al. have noted that the increased incidence may be

the result of higher prevalence of risk factors for this condition, lower prevalence of protective factors, or both (9). These factors are discussed below.

Recent trends have enabled health-care providers to become more aware of ectopic pregnancy and of the symptoms and signs that may occur among women of childbearing age. Additionally, technologic advances (such as ready availability of quantitative serum pregnancy hormone tests, improved imaging techniques (ultrasound), and laparoscopy for diagnosis and treatment) have led to the earlier diagnosis of some ectopic pregnancies and, ultimately, earlier intervention and better outcome. Although heightened awareness and technology may result in earlier diagnosis and management, they alone cannot explain the large increase in the number of ectopic pregnancies. Another possible factor contributing to the increased frequency is that, in recent years, many women have postponed childbearing until the period of life in which the risk of ectopic pregnancy is highest (10).

Ectopic pregnancy was first described in the 10th century (11). The etiology of the condition has been variously described as involving multiple maternal and embryonic factors (2,11,12). The effects that contraceptive methods may have on susceptibility to ectopic pregnancies have been extensively studied. Pregnancies among women who have used oral contraceptives in the past are not more likely to be ectopic than are pregnancies among women who have never used birth control pills (13). Studies on the use of pills at the time of conception have suggested an increased risk of ectopic pregnancy among progestogen-only (minipill) users (14). Other studies in which the type of pill was not specified showed either no effect or a protective effect against ectopic pregnancy (9).

Because intrauterine devices (IUDs) decrease the overall incidence of pregnancy, they have been shown to be protective against ectopic pregnancy. Although IUDs are protective against all pregnancies, they have been associated with a higher risk of ectopic pregnancy among women who conceive and do not abort (spontaneously or by induced abortion) while they are still using an IUD (9). Laboratory studies suggest that this association may be due either to physiologic changes in tubal motility or ovum transport or to hormonal influences (9). One large case-control study showed no difference in the risks of ectopic pregnancy for users and for nonusers of IUDs (15). In addition, the risk was lower for persons with a current in situ IUD than for those with a history of IUD use (15). This relationship may be explained by the link between IUD use and the occurrence of acute and chronic salpingitis. The prevalence of salpingitis, in relation to ectopic pregnancies, has been shown to vary widely (20%-92%) (5,9). In view of this association and of the fact that sexually transmitted diseases (STDs) appear to increase the risk of salpingitis, exposure to the organisms that cause STDs might also increase the risk of ectopic pregnancy.

Barrier contraceptives appear to decrease the risk of ectopic pregnancy by decreasing the occurrence of both pregnancy and STDs (16).

With more women choosing tubal sterilization as a means of contraception, scientific knowledge of the long-term risk of ectopic pregnancy with this method will increase. Although poststerilization pregnancies are infrequent, the ones that do occur are more likely to be ectopic than pregnancies among women who are not sterilized. In one study, 176 pregnancies occurred among 37,100 women who had undergone tubal sterilization (13). The incidence of ectopic pregnancy for these pregnancies was 16% (n = 28) for all sterilization methods and 20% (n = 14) for those performed by laparoscopy. Overall, these small numbers appear to account for very little of the large increase in the number of ectopic pregnancies.

In 1983, the risk of ectopic pregnancy for women of black and other races was decreasing toward being equal to the risk for white women. By 1985, however, the risk for women of black and other races had increased from 1.1 in 1983 to 1.6 times the risk for white women (3). In addition to this widening gap, black and other teenagers continue to have a higher rate of deaths related to ectopic pregnancy, 5.5 times that of white teenagers. Factors including timing and quality of prenatal care are often related to such deaths. Even though new technology may be helping to eliminate many deaths caused by ectopic pregnancies, women of black and other races and younger women, who tend to have less and later prenatal care, are not benefitting from this technology as much as other women (17,18).

The number of ectopic pregnancies reported here, although on the increase, may be underreported. The NHDS does not include medical records of patients discharged from federally operated hospitals, such as Armed Forces and Public Health Service hospitals. Furthermore, some ectopic pregnancies are known to resolve spontaneously and, so, are never diagnosed; and with some new treatment methods, hospitalization is not required. On the other hand, total pregnancies used as denominators are underestimated, since spontaneous abortions and stillbirths are not included. Moreover, the number of induced abortions reported to CDC have consistently been less than the numbers reported by private sources who obtained data by direct survey of providers of legal abortion (19). As a result of a smaller denominator, the rates of ectopic pregnancy may be elevated. However, because the method used for collecting data was consistent over the 16-year study period, the data reported here are believed to reflect actual occurrences in the United States.


  1. Centers for Disease Control. Ectopic Pregnancy--United

States, 1984-1985. MMWR 1988;37:637-9. 2. Pritchard JA, MacDonald PC, Gant NF. Williams obstetrics. 17th ed. Norwalk, Connecticut: Appleton-Century Croft, 1985:423-38. 3. Centers for Disease Control. Ectopic pregnancy surveillance, 1970-1978. Atlanta, Georgia: CDC, July 1982.

4. Centers for Disease Control. Ectopic pregnancy in the United States, 1979-1980. In: CDC surveillance summaries. MMWR 1984;33(no.2SS):1SS-7SS.

5. Centers for Disease Control. Ectopic pregnancy in the United States, 1970-1983. In: CDC surveillance summaries, August 1986. MMWR 1986;35(no.2SS):29SS-37SS.

6. International classification of diseases, eighth revision, adapted for use in the United States. Washington, DC: National Center for Health Statistics, 1967.

7. International classification of diseases, ninth revision, adapted for use in the United States. Ann Arbor, Michigan: National Center for Health Statistics and the Commission on Professional and Hospital Activities, 1978.

8. National Center for Health Statistics. Vital statistics of the United States, 1985. Vol. 1, natality. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, 1988:1,53.

9. Chow WH, Daling JR, Cates W Jr, Greenberg RS. Epidemiology of ectopic pregnancy. Epidemiol Rev 1987;9:70-94. 10. Pebley AR. Changing attitudes toward the timing of first births. Fam Plann Perspect 1981;13:171-5. 11. Weckstein LN. Current perspective on ectopic pregnancy. Obstet Gynecol Surv 1985; 40:259-72. 12. Barnes AB, Wennberg CN, Barnes BA. Ectopic pregnancy: incidence and review of determinant factors. Obstet Gynecol Surv 1983;38:345-56. 13. Tatum HJ, Schmidt FH. Contraceptive and sterilization practices and extra-uterine pregnancy: a realistic perspective. Fertil Steril 1977;28:407-21. 14. Luikko P, Erkola R, Laasko L. Ectopic pregnancies during use of low-dose progestogens for oral contraception. Contraception 1977;16:575-80. 15. Ory HW, et al. (Women's Health Study). Ectopic pregnancy and intrauterine contraceptive devices: new perspectives. Obstet Gynecol 1981;57:137-44. 16. Kelaghan J, Rubin GL, Ory HW, Layde PM. Barrier-method contraceptives and pelvic inflammatory disease. JAMA 1982;248:184-7. 17. National Center for Health Statistics. Health, United States, 1984. DHHS publication no. (PHS)85-1232. Hyattsville, Maryland: NCHS, 1984:10,11. 18. National Center for Health Statistics. Health, United States, 1986. DHHS publication no.(PHS)87-1232. Hyattsville, Maryland: NCHS, 1986:25. 19. Tietze C, Henshaw SK. Induced abortion: a world review, 1986 (6th ed). New York, New York: The Alan Guttmacher Institute, 1986.

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